BERLIN (AP) — German prosecutors have searched over a dozen offices and homes across the country as part of their investigation into a massive tax fraud going back more than a decade.

The scheme involved so-called cum-ex transactions in which participants would lend each other shares so they could collect reimbursement for taxes they hadn't paid, costing taxpayers across Europe billions of euros.

Frankfurt prosecutors said Thursday that about 170 officers raided 19 premises in four German states Tuesday.

In total, German authorities are conducting 10 separate investigations into cum-ex schemes, some of which involve bank employees.

A court in Switzerland is due to issue a verdict Thursday against three Germans accused of "economic espionage" for blowing the lid on the tax scheme by publishing documents revealing a Swiss bank's involvement.